The present invention relates to a fuel injector for injecting fuel into an engine, and more particularly to a so-called side-feed type fuel injector in which the fuel from a fuel tank is supplied into the injector through a fuel inlet formed through a side portion of an injector casing of the injector.
FIG. 5A is a vertical sectional view of such a side-feed type fuel injector in the prior art. Referring to FIG. 5A, a fuel injector 101 of a side-feed type is engaged through O-rings 104 and 105 to a mounting hole 102a of a jacket 102. The jacket 102 has a fuel passage 102b which is connected through a delivery pipe (not shown) and a fuel pump (not shown) to a fuel tank (not shown). The injector 101 has a fuel inlet 124 at its side portion, and the fuel from the fuel passage 102b is supplied through the fuel inlet 124 into the injector 101.
FIG. 5B shows an enlarged sectional view of a part of the side-feed type fuel injector 101 mounting a cylindrical strainer 123. Referring to FIG. 5B, an injector casing 111 is formed at its side portion with the fuel inlet 124. The cylindrical strainer 123 is fixedly mounted on an outer circumference of the injector casing 111 in such a manner as to cover the fuel inlet 124. The jacket 102 is so mounted as to surround the injector 101, and is adapted to be mounted to an engine (not shown). The jacket 102 is formed with a fuel passage 102b for feeding a pressurized fuel through the strainer 123 to the fuel inlet 124. The fuel is then fed into a valve housing 113 through a fuel groove 125 formed at a rear end of the valve housing 113. Thereafter, the fuel is injected from a fuel injection hole 113b shown in FIG. 5A by a valve 115 adapted to be driven by a driving means and thereby reciprocated in a guide hole 113a defined in the valve housing 113. The driving means is comprised of an armature 116 fixed to a rear end of the valve 115, a solenoid core 114 mounted in the injector casing 111, a solenoid coil 118 wound around the solenoid core 114, and a return spring 121 for normally biasing the valve 115 in a valve closing direction.
The strainer 123 is comprised of a synthetic resin frame 132 and a fine-mesh screen 131 attached to a side portion of the frame 132. The frame 132 is formed at its front and rear ends with annular portions 132a and 132b. The annular portions 132a and 132b are press-fitted with the outer circumference of the injector casing 111. However, since the synthetic resin frame 132 tends to generate creep as time proceeds, and particularly there is a possibility that a gap will be defined between the rear annular portion 132b and the outer circumference of the injector casing 111 because of the resin creep. As a result, there occurs a problem that the fuel will directly enter the injector 101 from the gap as well as through the fine-mesh screen 131, thus allowing a foreign matter contained in the fuel to enter the injector 101. A similar construction is disclosed in Japanese Utility Model Laid-open Publication No. 60-110674, for example.
To cope with the above-mentioned problem, there has been proposed a construction as shown in FIG. 6. Referring to FIG. 6, the injector casing 111 is formed at its outer circumference with an annular projection 111a, so that the rear annular portion 132b of the synthetic resin frame 132 may be urged against a front end surface of the annular projection 111a by a frictional force due to the interference fit between the front annular portion 132a and the outer circumference of the injector casing 111. However, when the front annular portion 132a of the frame 132 generates the resin creep, the strainer 123 will be slipped to cause the generation of a gap between the rear annular portion 132b and the front end surface of the annular projection 111a.
To improve the construction shown in FIG. 6, there has been proposed a further construction as shown in FIG. 7. Referring to FIG. 7, the annular projection 111a of the injector casing 111 is formed with a shoulder 111b, so that the rear annular portion 132b of the synthetic resin frame 132 is press-fitted with the shoulder 111b, and simultaneously the rear end surface of the rear annular portion 132b is urged against the front end surface of the annular projection 111a. However, when the front annular portion 132a of the frame 132 generates the resin creep, and the rear annular portion 132b of the frame 132 also generates the resin creep, the strainer 123 will be yet slipped to cause a gap between the rear annular portion 132b and the front end surface of the annular projection 111a.